Honeycomb-shaped straight-flow structure for catalyst and catalyst for purifying exhaust gases

Abstract

A honeycomb-shaped substrate for catalyst is made from ceramic, has a straight-flow structure, and includes cellular walls exhibiting pore volumes, which differ partially, and a large number of cellular passages demarcated by the cellular walls. A catalyst for purifying exhaust gases is produced by providing the cellular walls of the honeycomb-shaped substrate with a catalytic coating layer.

1. A honeycomb-shaped straight-flow structure for a catalyst, comprising:
 a plurality of cellular walls 
 a plurality of cellular passages demarcated by the cellular walls, said cellular passages having inlets and outlets, wherein said inlets and outlets of each cellular passage are open-ended, and 
 wherein a plurality of pores exhibiting unequal pore volumes are defined in portions of the cellular walls having a first side demarcating one of the cellular passages and a second side opposite the first side and demarcating another of the cellular passages, the pore volumes being greater on an exhaust-gas-flow upstream side of the honeycomb-shaped straight-flow structure than on an exhaust-gas-flow downstream side thereof; and 
 a coating layer coating a surface of the cellular walls and the pores of the honeycomb-shaped straight-flow structure, wherein the coating layer has a thickness on the exhaust-gas-flow upstream side of the honeycomb-shaped straight-flow structure greater than a thickness on the exhaust-gas-flow downstream side thereof. 
 
     
     
       2. The honeycomb-shaped straight-flow structure for a catalyst, according to  claim 1 , wherein: the pore volumes are exhibited by fine pores whose pore diameters are 2 μm or less. 
     
     
       3. A catalyst for purifying exhaust gases, comprising:
 a honeycomb-shaped straight-flow structure, comprising:
 a plurality of cellular walls; 
 a plurality of cellular passages demarcated by the cellular walls, said cellular passages having inlets and outlets, wherein said inlets and outlets of each cellular passage are open-ended, and 
 wherein a plurality of pores exhibiting unequal pore volumes are defined in portions of the cellular walls having a first side demarcating one of the cellular passages and a second side opposite the first side and demarcating another of the cellular passages, the pore volumes being greater on an exhaust-gas-flow upstream side of the honeycomb-shaped straight-flow structure than on an exhaust-gas-flow downstream side thereof; and 
 a coating layer coating a surface of the cellular walls and the pores of the honeycomb-shaped straight-flow structure, wherein the coating layer has a thickness on the exhaust-gas-flow upstream side of the honeycomb-shaped straight-flow structure greater than a thickness on the exhaust-gas-flow downstream side thereof; and 
 
 a catalytic ingredient is loaded on the coating layer. 
 
     
     
       4. The catalyst according to  claim 3 , wherein: the cellular walls have pore volumes greater on an outer peripheral side of the honeycomb-shaped straight-flow structure than on an inner peripheral side thereof; and
 the coating layer has a thickness on the outer peripheral side of the honeycomb-shaped straight-flow structure greater than a thickness on the inner peripheral side thereof. 
 
     
     
       5. The catalyst according to  claim 3 , wherein:
 the cellular walls have pore volumes greater at flat portions of the cellular walls than at proximate corners of the cellular walls; and 
 the coating layer has a thickness at the flat portions of the cellular walls greater than a thickness at the proximate corners of the cellular walls. 
 
     
     
       6. A honeycomb-shaped straight-flow structure for a catalyst, comprising:
 a plurality of cellular walls; 
 a plurality of cellular passages demarcated by the cellular walls, wherein said cellular passages are open-ended, 
 wherein a first plurality of pores are defined in outer portions of the cellular walls having a first side demarcating one of the cellular passages and a second side opposite the first side demarcating another of the cellular passages, and a second plurality of pores are defined in inner portions of the cellular walls having a first side demarcating one of the cellular passages and a second side opposite the first side demarcating another of the cellular passages, the outer portions of the cellular walls being closer than the inner portions of the cellular walls to a perimeter of the honeycomb-shaped straight-flow structure, and pore volumes of the first plurality of pores being greater than pore volumes of the second plurality of pores; and 
 a coating layer coating a surface of the cellular walls and the pores of the honeycomb-shaped straight-flow structure wherein the coating layer has a thickness on the outer portions of the cellular walls greater than a thickness on the inner portions of the cellular walls. 
 
     
     
       7. The honeycomb-shaped straight-flow structure for a catalyst, according to  claim 6 , wherein the pore volumes are exhibited by fine pores having pore diameters of 2 μm or less. 
     
     
       8. A catalyst for purifying exhaust gases, comprising:
 a honeycomb-shaped straight-flow structure, comprising:
 a plurality of cellular walls; 
 a plurality of cellular passages demarcated by the cellular walls, wherein said cellular passages are open-ended, 
 wherein a first plurality of pores are defined in outer portions of the cellular walls having a first side demarcating one of the cellular passages and a second side opposite the first side demarcating another of the cellular passages, and a second plurality of pores are defined in inner portions of the cellular walls having a first side demarcating one of the cellular passages and a second side opposite the first side demarcating another of the cellular passages, the outer portions of the cellular walls being closer than the inner portions of the cellular walls to a perimeter of the honeycomb-shaped straight-flow structure, and pore volumes of the first plurality of pores being greater than pore volumes of the second plurality of pores; and 
 a coating layer coating a surface of the cellular walls and the pores of the honeycomb-shaped straight-flow structure wherein the coating layer has a thickness on the outer portions of the cellular walls greater than a thickness on the inner portions of the cellular walls; and 
 
 a catalytic ingredient is loaded on the coating layer. 
 
     
     
       9. The honeycomb-shaped straight-flow structure for a catalyst, according to  claim 1 , wherein:
 the cellular walls have pore volumes greater on an outer peripheral side of the honeycomb-shaped straight-flow structure than on an inner peripheral side thereof; and 
 the coating layer has a thickness on the outer peripheral side of the honeycomb-shaped straight-flow structure greater than a thickness on the inner peripheral side thereof. 
 
     
     
       10. The honeycomb-shaped straight-flow structure for a catalyst, according to  claim 1 , wherein:
 the cellular walls have pore volumes greater at flat portions of the cellular walls than at proximate corners of the cellular walls; and 
 the coating layer has a thickness at the flat portions of the cellular walls greater than a thickness at the proximate corners of the cellular walls. 
 
     
     
       11. The catalyst according to  claim 3 , wherein:
 the pore volumes are exhibited by fine pores having pore diameters of 2 μm or less. 
 
     
     
       12. The honeycomb-shaped straight-flow structure for a catalyst, according to  claim 6 , wherein:
 the cellular walls have pore volumes greater on an exhaust-gas-flow upstream side of the honeycomb-shaped straight-flow structure than on an exhaust-gas-flow downstream side thereof; and 
 the coating layer has a thickness on the exhaust-gas-flow upstream side of the honeycomb-shaped straight-flow structure greater than a thickness on the exhaust-gas-flow downstream side thereof. 
 
     
     
       13. The honeycomb-shaped straight-flow structure for a catalyst, according to  claim 6 , wherein:
 the cellular walls have pore volumes greater at flat portions of the cellular walls than at proximate corners of the cellular walls; and 
 the coating layer has a thickness at the flat portions of the cellular walls greater than a thickness at the proximate corners of the cellular walls. 
 
     
     
       14. The catalyst according to  claim 8 , wherein:
 the pore volumes are exhibited by fine pores having pore diameters of 2 μm or less. 
 
     
     
       15. The catalyst according to  claim 8 , wherein:
 the cellular walls have pore volumes greater on an exhaust-gas-flow upstream side of the honeycomb-shaped straight-flow structure than on an exhaust-gas-flow downstream side thereof; and 
 the coating layer has a thickness on the exhaust-gas-flow upstream side of the honeycomb-shaped straight-flow structure greater than a thickness on the exhaust-gas-flow downstream side thereof. 
 
     
     
       16. The catalyst according to  claim 8 , wherein:
 the cellular walls have pore volumes greater at flat portions of the cellular walls than at proximate corners of the cellular walls; and 
 the coating layer has a thickness at the flat portions of the cellular walls greater than a thickness at the proximate corners of the cellular walls. 
 
     
     
       17. The honeycomb-shaped straight-flow structure for a catalyst, according to  claim 1 , wherein the coating layer is composed of an identical material along an entire length of the honeycomb-shaped straight-flow structure. 
     
     
       18. The catalyst according to  claim 3 , wherein the coating layer is composed of an identical material along an entire length of the honeycomb-shaped straight-flow structure. 
     
     
       19. The honeycomb-shaped straight-flow structure for a catalyst, according to  claim 6 , wherein the coating layer is composed of an identical material along an entire length of the honeycomb-shaped straight-flow structure. 
     
     
       20. The catalyst according to  claim 8 , wherein the coating layer is composed of an identical material along an entire length of the honeycomb-shaped straight-flow structure.